Automatic underwater bracing system for a mobile drilling rig



J1me 1958 w. H. NEDDERMAN ETAL 2,837,897

AUTOMATIC UNDERWATER BRACING SYSTEM FOR A MOBILE DRILLING RIG 2Sheets-Sheet 1 Filed Sept. 24, 1954 FI G. 1.

FIG. 2

P TTORNEY June 10, 1958 w. H. NEDDERMAN EI'AL 2,837,897

AUTOMATIC UNDERWATER BRACING SYSTEM FOR A MOBILE DRILLING RIG FiledSept. 24, 1954 2 Sheets-Sheet 2 25 26k 11 i 1L i E 10 u I l 'l [I H II n"25:? ?ii I! 5% I '5' 21 22 ;i 11 1 ii 16{ I 14! 1 l 25" f -26 L 17f LINVENTORS w 5' NE PMYQN RT-LIET i-XTTOPNEY United States PatentAUTOMATIC UNDERWATER BRACING SYSTEM FOR A MOBILE DRILLING RIG Wendell H.Nedderman, College Station, and Richard T. Lietz, Houston, Tex.,assignors, by direct and mesne assignments, to Gulf Oil Corporation,Pittsburgh, Pa., a corporation of Pennsylvania Application September 24,1954, Serial No. 458,178

3 Claims. (Cl. til-46.5)

This invention relates to an automatic underwater bracing system for amobile drilling platform which is floated to the site of drillingoperations and is there raised and supported on tubular columns orpilings which are lowered to bottom. The mobile structure may includes asubmersible barge serving as a foundation unit from which uprightcolumns extend to project above water when the foundation unit rests onbottom and upon which columns the platform is elevated to a positionsufiiciently high above water level to be out of the reach of waves.

Such a structure is constantly subjected to lateral forces of varyingmagnitude and direction which are imposed upon it by wind and water andit must additionally carry heavy loads. Bracing of the relatively thinand long supporting columns is therefore required to impart rigidity tothe structure, and especially where the installation is made inrelatively deep water, say 70 to 140 feet, the problem arises oferecting underwater braces for the submerged lengths of the supportingcolumns without restort to the services of a diver or to the use ofcomplicated and expensive clamping means remotely controlled from theplatform.

The present invention has as one of its objects to provide an underwaterbracing system which is initially collapsed but which is automaticallyerected between the supporting columns as they are being lowered tobottom.

For the purpose of illustrating the system of bracing without, however,limiting the invention in its application to the particular type ofmobile structure illustrated, the accompanying drawings, showingend'elevations in all figures, are as follows:

Figure 1 shows a platform having a foundation barge drawn up to itsunder side, in which position the structure may be towed to a desiredlocation with the bracing system collapsed and stowed between theplatform and the underlying submersible foundation.

Figure 2 shows the mobile unit at a drilling site, the foundation bargebeing lowered part way to bottom and the bracing system partiallyerected.

Figure 3 shows the mobile unit with "the foundation barge resting onbottom and with the platform floating,-

in which position the bracing system is fully erected.

Figure 4 shows the structure in final position with the platformelevated above water level.

Referring more particularly to the drawings, a platform which maycomprise a buoyant hull is provided with a series of wells 11 throughwhich tubular columns or pilings 12 extend. The lower ends of thecolumns are permanently built into an underlying foundation barge 13which can be flooded and sunk to rest on bottom when the platform is indesired location. Tubular braces 14 and 15 extend horizontally betweenadjacent columns 12 and at their panel points they carry rings or shorttubular sections which encircle the columns and are slidable thereon butwithout appreciable looseness of fit. These braces 14 and 15 constituteopposite sides of a truss panel between the adjacent supporting columns.Chain or wire cables 17 and 18 extend diagonally between the ends of thehorizontal braces 14 and 15, as cross-tie elements, and similar cables19 and 20 extend between the brace 15 and the foundation barge 13 towhich they are permanently fastened, there being as many of thesehorizontal braces, and consequently as many truss panels, as may berequired, depending upon the length of the supporting columns.

Cables 21 and 22 which are fastened to the opposite ends of thehorizontal brace 14 pass upwardly through the wells 11 in the platform,or through separate wells provided therefor, and over sheaves 23 and 24mounted on the upper ends of the columns 12. counterweights 25 and 26 towhich the cables 21 and 22 are attached may suitably ride within thehollow columns, these cables being arranged to be engaged byplatform-mounted clamps 27 after the platform has been elevated to thedesired height by jacks (not shown) which grip the columns, or by othersuitable lifting means such as block and tackle, gearing, etc. Thus, inFigures 1 to 3, the clamps 27 are shown open so that the cables may ridefreely therethrough while in Figure'4 they are shown closed on thecables.

As illustrated in Figure, 1, the rig is in towing position. The cables21 and 22 are held taut by the counterweights 25 and 26 which are freelyslidable in the columns 12, whereby they assist in drawing thehorizontal brace 14 up to the under side of the platform which may besuitably recessed to receive it as well as the similar horizontal brace15, the cross bracing cables 17 and 20 being slack. it is within thepurview of this invention that the foundation barge, instead, may berecessed in its upper surface for stowing the collapsed bracing system.

When the foundation barge is lowered to bottom, as shown in successivestages in Figures 2 and 3, the lowermost brace 15 drops with thefoundation barge, the upper horizontal brace 14 being restrained by thecounterweights. Thus, the crossed cables 17 and 18 are pulled taut andas the foundation barge continues to sink, the crossed cables 19 and 20are likewise tightened and the upper horizontal brace 14 is drawn downagainst the upward pull of the counterweights exerted through the cables21 and 22. The counterweights additionally have a cushioning actionwhich avoids sudden shock or impact as slack is taken out of the crossedcables and they reach their full extension.

With the foundation barge resting on bottom, the counterweights hold theunderwater bracing system in extended condition under tension. For thispurpose, the size of the counterweights is selected according to theweight and number of cross-braced units or truss panels. The submergedweight of the horizontal braces alone will be relatively small sincethese members are tubular and closed at their ends, and so haveconsiderable buoyancy.

The platform is next elevated above water level on the columns by meansof jacks, block and tackle, gearing or other conventional mechanismwhich is suitable for the purpose. When the platform has reached adesired height, slips (not shown) are set to grip the column and preventits retrograde movement. Clamps which are mounted on the platform andindicated generally at 27 in the drawings are manipulated to grip thecables 21 and 22, as shown in Figure 4, whereby the bracing system ismaintained under the desired tension for its adequate functioning. Wherenecessary, the counterweights may be removed from certain of the hollowcolumns after the platform has been secured in elevated position and thecables 21 and 22 have been clamped as aforesaid. The necessity forremoving the counterweights from the hollow Columns may be expected toarise only where the design of the platform requires that spud piling bedriven through certain of the B3 supporting columns, in which case thecounterweights would constitute an obstruction.

As an alternative to the use of countcrweights, a winch may be mountedon the platform to haul up and thereby erect the underwater bracingsystem after the foundation barge has been lowered, and to hold thebracing system at its proper location on the pilings.

The lengths of the crossed cables and the number of horizontal bracesbetween which they extend will depend upon the expected range ofoperating depths for the platform. Should it be desired to utilize onlythe upper unit of the bracing system, provision may be made fortemporarily securing the horizontal brace to the foundation barge tohold the lower truss panel in collapsed c0ndition. The abbreviatedbracing system thus provided may be used where operations are conductedin relatively shallow water.

While the invention contemplates the use of either chain or wire cablefor the cross members, heavy anchor chain is desirable for the purposesince it has less tendency to snarl and tangle when stowed. The liftingcables 21 and 22 are desirably of high tensile strength steel wire.

From the foregoing it will be understood that when the foundation bargeis lowered the bracing system is automatically brought into the properposition under the pull exerted by the lower diagonal crossed cableswhich are fastened to the foundation unit and the opposing pull of thecounterweights on the top horizontal brace member. As thus erected, thesystem affords adequate bracing for the columns without requiringlaborious clamping procedures, yet it may be collapsed with facility andconveniently stowed when the platform is to be moved to a differentlocation.

What we claim is:

1. In combination with a platform supported over water on a plurality ofcolumns which are lowered to bottom and partly submerged, anautomatically erected underwater bracing system for the supportingcolumns comprising a number of rigid brace members extendinghorizontally between the adjacent columns and having rings at their endsencircling the columns and permitting the brace members to movetherealong, cross cables connecting adjacent brace members, said crosscables being of such flexibility that the connected brace members may becollapsed together and stowed in stacked relation, further flexiblecross cables attached at one end to the lowermost brace member andanchored at their opposite ends in fixed relation to the columns wherebythey are placed under tension as the columns are lowered, and meansexerting an upward pull on the uppermost horizontal brace member as thelowermost brace member is pulled downwardly in lowering the supportingcolumns,'whereby the flexible cross cables of the bracing system areplaced under tension.

4 l 2. In combination with a platform supported over Water on aplurality of columns which are lowered to bottom and upon which theplatform is elevated above water level, an automatically erectedunderwater bracing system for the supporting columns comprising rigidbrace members extending horizontally between the adjacent columns andhaving rings at their ends encircling the columns, and enabling thebrace members to move there along, cross cables extending diagonallybetween the brace members and because of their flexibility permittingthe brace members to be collapsed together and stowed in stackedrelation, further cross cables attached at one end to the lowermostbrace member and anchored at their opposite ends in fixed relation tothe columns, whereby they are placed under tension as the columns arelowered, cables passing upwardly from the uppermost brace member andover sheaves carried by the columns, and counterweights on saidlast-named cables exerting an upward pull on the extended bracing systemsufiicicnt to maintain tension on the diagonally extending cross cablesthereof. 3. In combination with a platform supported over water on aplurality of columns projecting from a submersible barge which whensunl: serves as a foundation resting on bottom, an automatically erectedbracing system for the supporting columns comprising a plurality ofrigid brace members extending between pairs of adjacent columns andhaving rings at their ends encircling the columns to permit relativevertical movements of the brace members, diagonally crossed cablesconnecting each brace member with the next in series and, because oftheir flexibility, permitting the series of brace members to becollapsed together and stowed between the platform and submersiblestructure drawn up thereto in moving to location, cables passingupwardly from the uppermost brace member and over sheaves mounted on thecolumns above the platform, counterweights on said cables exerting anupward pull on the bracing system, crossed cables connecting thelowermost brace member to the submersible structure and serving to drawthe bracing system of cross cables taut against the upward pull of thecounterweights as the fundation structure is sunk, and fastening meanson the foundation structure for securing a lower brace member andthereby selectively shortening the span of the extended bracing system.

References Cited in the file of this patent UNITED STATES PATENTS

